Reflective liquid crystal spatial light modulator and projection apparatus comprising same

Abstract

Reflective spatial light modulators (RSLMs) and projection apparatus employing such RSLMs are disclosed. The RSLM comprises a reflective surface and a superposed light-modulation layer. The reflective surface is configured to have a reflective diffraction optical element or a microfaceted reflective array. Incident light impinging on the RSLM can pass through the light-modulation layer, reflect from the reflective surface, and return through the light-modulation layer to become modulated signal light capable of forming a viewable image if projected onto a screen or other surface. The reflective diffraction optical element or microfaceted reflective array on the reflective surface is operable to cause the signal light to propagate from the RSLM in a different direction than any ghost light reflected from the RSLM. Projection apparatus employing such an RSLM comprise an illumination optical system, a projection optical system that may or may not be coaxial with the illumination optical system, and a stop operable to pass signal light but not ghost light to a screen for viewing. The viewed image has enhanced contrast over the prior art.

What is claimed is: 
     
       1. A projection apparatus, comprising: (a) an illumination optical system operable to provide an illumination light flux;   (b) a reflective spatial light modulator positioned to receive the illumination light flux, the reflection spatial light modulator comprising a reflective surface, a light-modulation layer superposed on the reflective surface, the light-modulation layer being operable to produce a signal light from incident light impinging on the reflective spatial light modulator, the signal light being propagated by the reflective spatial light modulator in a direction sufficiently different from any ghost light reflected from the reflective spatial light modulator so as to allow the ghost light to be blocked relative to the signal light;   (c) a stop defining an aperture, the stop being positioned so as to allow passage through the aperture of the signal light propagated by the reflection spatial light modulator, but not the ghost light; and   (d) a reflective diffraction optical element situated on the reflective surface of the reflective spatial light modulator, wherein the reflective diffraction optical element comprises an array of phase shifters operable to produce higher orders of diffracted signal light that propagate from the reflective spatial light modulator in different directions than the ghost light, and to cancel zeroth-order diffracted light.   
     
     
       2. The projection apparatus of claim 1, wherein the reflective spatial light modulator further comprises a microfaceted reflective array on the reflective surface. 
     
     
       3. The projection apparatus of claim 2, wherein the microfaceted reflective array comprises a regular array of pyramids. 
     
     
       4. The projection apparatus of claim 2, wherein the microfaceted reflective array comprises a regular array of longitudinal valleys and ridges. 
     
     
       5. A projection apparatus comprising: (a) an illumination optical system operable to provide an illumination light flux;   (b) a reflective spatial light modulator positioned to receive the illumination light flux, the reflection spatial light modulator comprising a reflective surface, a light-modulation layer superposed on the reflective surface, the light-modulation layer being operable to produce a signal light from incident light impinging on the reflective spatial light modulator, the signal light being propagated by the reflective spatial light modulator in a direction sufficiently different from any ghost light reflected from the reflective spatial light modulator so as to allow the ghost light to be blocked relative to the signal light;   (c) a stop defining an aperture, the stop being positioned so as to allow passage through the aperture of the signal light propagated by the reflection spatial light modulator, but not the ghost light; and   (d) a microfaceted reflective array on the reflective surface of the reflective spatial light modulator, the microfaceted reflective array comprising a regular array of cones.   
     
     
       6. A reflective spatial light modulator, comprising: (a) a reflective surface;   (b) a light-modulation layer superposed on the reflective surface, the light-modulation layer being operable to modulate incident light passing through the light-modulation layer so as to produce a signal light;   (c) a transparent layer superposed on the light-modulation layer; and   (d) a reflective diffraction optical element on the reflective surface operable to produce higher diffraction orders of signal light and to substantially cancel zero-order signal light.   
     
     
       7. The reflective spatial light modulator of claim 6, operable to propagate the higher orders of signal light from the reflective spatial light modulator in directions that are sufficiently different from any ghost light reflected from the reflective spatial light modulator so as to allow the ghost light to be blocked relative to the higher orders of signal light. 
     
     
       8. The reflective spatial light modulator of claim 6, wherein the reflective optical element comprises phase shifters situated in a regular array on the reflective surface. 
     
     
       9. The reflective spatial light modulator of claim 8, wherein each phase shifter is operable to impart a phase shift of about λ/2 to light of wavelength λ passing through the phase shifter, reflecting from the reflective surface, and returning through the phase shifter, compared to light reflecting from the reflective surface without passing through the phase shifter. 
     
     
       10. The reflective spatial light modulator of claim 6, wherein the reflective optical element comprises a regular array of indentations and protrusions arranged on the reflective surface, the indentations and protrusions being configured to impart a phase shift of about λ/2 to light of wavelength λ reflecting from an indentation compared to light of wavelength λ reflecting from a protrusion. 
     
     
       11. A projection apparatus comprising: (a) an illumination optical system operable to provide an illumination light flux;   (b) a projection optical system operable to project a signal light flux to a viewing surface, the illumination optical system and the projection optical system being coaxial with each other; and   (c) a reflective spatial light modulator situated relative to the illumination optical system and the projection optical system so as to produce the signal light flux from the illumination light flux impinging on the reflective spatial light modulator and to direct the signal light flux to the projection optical system, the reflective spatial light modulator (i) comprising a reflective surface and a light-modulation layer superposed on the reflective surface, and (ii) canceling signal light of a specific order by interference with light of a different phase, while directing the signal light of another order that is different from that of the specific order, to the viewing surface.   
     
     
       12. The projection apparatus of claim 11, wherein the illumination-light flux impinges upon the reflective spatial light modulator normal to the reflective spatial light modulator. 
     
     
       13. The projection apparatus of claim 11, wherein the reflective spatial light modulator comprises a reflective diffraction optical element. 
     
     
       14. The projection apparatus of claim 13, wherein the reflective diffraction optical element comprises phase shifters arrayed in a regular pattern on the reflective surface, each phase shifter being operable to impart a phase shift of about λ/2 to light of wavelength λ passing through the phase shifter, reflecting from the reflective surface, and returning through the phase shifter, compared to light reflecting from the reflective surface without passing through the phase shifter. 
     
     
       15. The projection apparatus of claim 13, wherein the reflective diffraction optical element comprises a regular array of indentations and protrusions arranged on the reflective surface, the indentations and protrusions being configured to impart a phase shift of about λ/2 to light of wavelength λ reflecting from an indentation compared to light of wavelength λ reflecting from a protrusion. 
     
     
       16. The projection apparatus of claim 11, wherein the reflective spatial light modulator comprises a microfaceted reflective array on the reflective surface. 
     
     
       17. The projection apparatus of claim 11, wherein the projection optical system comprises, in order from the reflective spatial light modulator side, a first lens group, an exit-side aperture, and a second lens group. 
     
     
       18. The projection apparatus of claim 17, wherein the illumination optical system comprises an illumination-side aperture situated between the first lens group and the second lens group such that the illumination-light flux passes through the illumination-side aperture to be refracted by the first lens group for impingement on the reflective spatial light modulator. 
     
     
       19. The projection apparatus of claim 18, wherein the exit-side aperture is situated between the first lens group and the second lens group such that the signal light flux, but substantially no ghost light, passes through the exit-side aperture to be refracted by the second lens group for impingement on the viewing surface. 
     
     
       20. The projection apparatus of claim 19, wherein the illumination-side aperture and the exit-side aperture are defined by a stop disposed between the first and second lens groups. 
     
     
       21. The projection apparatus of claim 20, wherein the stop is operable to block the ghost light while allowing the signal light flux to pass through the exit-side aperture to the viewing surface. 
     
     
       22. The projection apparatus of claim 20, wherein the stop is operable to pass ghost light back through the illumination-side aperture rather than the exit-side aperture, thereby preventing the ghost light from reaching the viewing surface.